Network Glossary B

B8ZS See Bipolar 8 Zero Substitution.

backbone area (OSPF) Area 0; the area to which all other OSPF areas much connect in order for OSPF to work.

BackboneFast Cisco-proprietary STP feature in which switches use messaging to confirm the loss of Hello BPDUs in a switch’s Root Port, to avoid having to wait for maxage to expire, resulting in faster convergence.

backup designated router In OSPF, a router that is prepared to take over the designated router.

backup state An 802.1w RSTP port state in which the port is an alternative Designated Port on some LAN segment.

Backward Explicit Congestion Notification A bit inside the Frame Relay header that, when set, implies that congestion occurred in the direction opposite (or backward) as compared with the direction of the frame.

Bc See Committed Burst.

Bc bucket Jargon used to refer to the first of two buckets in the dual token bucket model; its
size is Bc.

BDR See backup designated router.

Be See Excess Burst.

Be bucket Jargon used to refer to the second of two buckets in the dual token bucket model; its
size is Be.

beacon An 802.11 frame that access points or stations in ad hoc networks send periodically so that wireless stations can discover the presence of a wireless LAN and coordinate use of certain protocols, such as power-save mode.

BECN See Backward Explicit Congestion Notification.

BGP See Border Gateway Protocol.

BGP decision process A set of rules by which BGP examines the details of multiple BGP routes for the same NLRI and chooses the single best BGP route to install in the local BGP table.

BGP table A table inside a router that holds the path attributes and NLRI known by the BGP implementation on that router.

BGP Update A BGP message that includes withdrawn routes, path attributes, and NLRI.

Bipolar 8 Zero Substitution A serial-line encoding standard that substitutes Bipolar Violations in a string of eight binary 0s to provide enough signal transitions to maintain synchronization.

Bipolar Violation For some encoding schemes, consecutive signals must use opposite polarity
in an effort to reduce DC current. A BPV occurs when consecutive signals are of the same polarity.

blocking state An 802.1d STP port state in which the port does not send or receive frames, except for listening for received Hello BPDUs.

boot field The low-order 4 bits of the configuration register. These bits direct a router to load either ROMMON software (boot field 0x0), RXBOOT software (boot field 0x1), or a full-function IOS image.

Boot Protocol A standard (RFC 951) protocol by which a LAN-attached host can dynamically broadcast a request for a server to assign it an IP address, along with other configuration settings, including a subnet mask and default gateway IP address.

BOOTP See Boot Protocol.

bootstrap router In multicast (IPv4 and IPv6), the process that associates multicast groups with rendezvous points (RPs) in PIM BSR mode.

Border Gateway Protocol An exterior routing protocol designed to exchange prefix information between different autonomous systems. The information includes a rich set of characteristics called path attributes, which in turn allows for great flexibility regarding routing choices.

BPDU Guard Cisco-proprietary STP feature in which a switch port monitors for STP BPDUs of any kind, err-disabling the port upon receipt of any BPDU.

BPV See Bipolar Violation.

broadcast address Ethernet MAC address that represents all devices on the LAN.

broadcast domain A set of all devices that receive broadcast frames originating from any device within the set. Devices in the same VLAN are in the same broadcast domain.

broadcast subnet When subnetting a class A, B, or C address, the subnet for which all subnet bits are binary 1.

BSR See bootstrap router.